The present invention relates to a valve movement control system of an internal combustion engine having a hydraulic operational characteristic variable mechanism for altering operational characteristic such as opening-closing time of an engine valve, including a hydraulic phase variable mechanism for altering opening-closing time of an engine valve such as a suction valve or an exhaust valve.
Hitherto, there has been known a valve movement control system of an internal combustion engine having a hydraulic phase variable mechanism which alters opening-closing time of a suction valve or an exhaust valve by altering relative phase of a camshaft to a crankshaft in accordance with operational state of the engine, in order to improve engine output and fuel consumption.
For example, in a valve timing control system of an internal combustion engine disclosed in Japanese Laid-Open Patent Publication Hei 11-173119, a valve timing adjusting mechanism provided on an end of a suction side camshaft has a rotor housing drivingly connected to a crankshaft and a vane rotor having a plurality of vanes drivingly connected to the suction side camshaft. On both sides of the each vane are formed a retard chamber and an advance chamber respectively, and charging and discharging of operating oil to the retard chamber and the advance chamber are controlled by a OCV (oil control valve) operated based on operational state of the engine, so that relative phase of the suction side camshaft to the crankshaft is altered to adjust opening-closing timing of the suction valve.
The operating oil supplied by an oil pump driven by the engine and controlled by the OCV is charged to or discharged from the retard chamber and the advance chamber, passing through a head oil passage provided in a cylinder head, an annular oil groove provided on an inner peripheral surface of a journal bearing formed by the cylinder head and a bearing cap for supporting the camshaft, and an oil passage provided in the camshaft.
Generally, a minute gap exists between the camshaft and the journal bearing. Therefore, in the prior art, when the engine is stopped to stop the oil pump and the operating oil is not supplied to the oil passage, the operating oil in the oil passage provided in the suction side camshaft and the operating oil in the retard chamber and the advance chamber flow out through the minute gap as time goes by, though by very small amount, so that the operating oil in the oil passage, the retard chamber and the advance chamber has a tendency to decrease.
When the engine is started from the state that operating oil in the oil passage, the retard chamber and the advance chamber is reduced, some waiting time is required after the engine is started to drive the oil pump, for filling the oil passage and the retard chamber or the advance chamber with the operating oil (whether any one chamber or both chambers must be filled with the operating oil depends on setting of the valve timing adjusting mechanism during the engine is stopped), and enabling the valve timing adjusting mechanism to operate. However, a time required for the engine to reach a loaded operation necessitating valve timing adjustment is relatively long in general and the oil passage and the retard chamber or the advance chamber can be filled with the operating oil during the time, therefore the above-mentioned required waiting time does not came into question.
However, on re-starting of the engine when the engine is started from a state that warming-up is completed, the time required for the engine to reach the loaded operation is relatively short in general, so that sometimes the oil passage and the retard chamber or the advance chamber are not filled with the operating oil before the engine reaches the loaded operation. In this case, the valve timing adjusting mechanism can not operate until the oil passage and the retard chamber or the advance chamber are filled with the operating oil. This late operation causes lowering of the engine output, and lowering of drive-ability in case of an engine mounted on a vehicle.